1. Field of the Invention
This invention relates to a transmission cable termination box, and a transmission cable installation and recovery method which is employed when installing transmission cables such as copper wire cables and optical fiber cables.
There is a strong demand to simplify the transmission cable installation process because of increasing use of transmission cables, such as optical fiber cables, in the communications industry. Transmission cables are often required to span great distances. In a conventional installation method, optical fiber cables are fused together to provide a transmission cable of the required length. Another installation method, uses optical fiber cables with connectors at the optical fiber cable ends. Optical fiber cables with connectors are delivered to a work site where they are connected to provide a transmission cable of sufficient length. The resulting transmission cable is often longer than required, and the extra transmission cable length must be dealt with.
It is not practical to produce transmission cables, such as optical fiber cables or copper wire cables, of different lengths to accurately obtain the exact length of the transmission cable required for a given installation. Therefore, techniques for accommodating the extra length of transmission cable have been developed.
2. Description of the Prior Art
When installing a transmission cable such as a copper wire cable or optical fiber cable, a predetermined length transmission cable is accommodated in a termination box. The cable is laid by being dram out of a working side of the termination box.
European Patent Application (OPI) No. 0296860 discloses an optical fiber cable accommodating container wherein the optical fiber cable is placed in the container by utilizing the cable's own weight to drop the cable into the container. During installation the optical fiber cable is pulled out of the container.
FIGS. 18 through 20 are explanatory diagrams showing a transmission cable accommodating unit disclosed by European Patent Application No. 0296860. More specifically, FIG. 18 is an explanatory diagram showing a transmission cable which is being accommodated within the transmission cable accommodating unit. FIG. 19 is an explanatory diagram showing the transmission cable which has been accommodated within the transmission cable accommodating unit. FIG. 20 is an explanatory diagram showing the transmission cable being pulled out of the transmission cable accommodating unit. In FIGS. 18 through 20, reference numeral 91 designates the transmission cable; 92, the transmission cable accommodating unit; 93, a central hole; 94, an upper guide; 95, a lower guide; 96, a drawing roller; 97, a roller drive force transmitting section; 98, a withdrawing angle adjusting device; 99, a gear 100, a drive motor; 101, a motor casing; 102, a cable taking device; and 103, a guide cap.
As shown in FIG. 20, the transmission cable accommodating unit 92 is cylindrical and has the aforementioned central hole 93 at its center. The central hole 93 is cylindrical and extends through the bottom of the transmission cable accommodating unit 92. Therefore, the transmission cable accommodating unit 92 has a transmission cable accommodating chamber, at the bottom, which is annular.
FIG. 18 shows the cable taking device 102 set on the transmission cable accommodating unit 92, the lower guide 95 set on the cable taking device 102, and the upper guide 94 set on the lower guide 95. The motor casing 101 is located at the center of the lower portion of the cable taking device 102 in such a manner that it is in the central hole 93 of the transmission cable accommodating unit 92. The drive motor 100 is provided in the motor casing 101, and the rotation of the drive motor 100 is transmitted through the gear 99 and the roller driving force transmitting section 97 to the drawing roller 96. The drawing roller 96 is rotated, drawing the transmission cable 91 down the upper guide 94 and along the locus 104 thereof. The gear 99 also applies torque to the drawing angle adjusting device 98, thus changing the angle of the drawing roller 96. Therefore, while the transmission cable 91 is drawn, position of locus 104 of the transmission cable 91 is shifted slightly.
FIG. 19 shows a part of the transmission cable 91 which has been accommodated in the transmission cable accommodating unit 92. As shown in FIG. 19, the transmission cable 91 is accommodated by being shifted in position. Once the transmission cable 91 has been accommodated in the transmission cable accommodating unit 92, the transmission cable accommodating unit 92 is disengaged from the cable taking device 102.
When installing the transmission cable, as shown in FIG. 20, the guide cap 103 is set on the transmission cable accommodating unit 92, and the transmission cable 91 is withdrawn through the hole in the guide cap 103.
To aid in understanding the withdrawal process, FIG. 20 illustrates the guide cap 103 removed obliquely above the transmission cable accommodating unit 102.
The above-described conventional technique is disadvantageous in the following ways:
(1) The transmission cable accommodating unit is bulky due to the drive motor being positioned at its center.
(2) The drawing roller's intricate motion requires a large number of components, and accordingly is high in manufacturing cost.
(3) For the same reason in (2), it is difficult to adjust the drawing roller.
(4) Since the transmission cable is dropped or drawn into the transmission cable accommodating unit by its own weight, it is necessary to provide a transmission cable accommodating unit with a considerably large floor area.
(5) Since the transmission cable is withdrawn from the transmission cable accommodating unit using the cap guide set on it as shown in FIG. 20, the cable drawing tension is unstable.
The noted disadvantages of the prior art transmission cable accommodating technique require the process of accommodating the transmission cable within the transmission cable accommodating unit to be performed at the factory. Therefore the prior art technique is not suitable for dealing with the extra length of transmission cable encountered during transmission cable installation.
Additionally, it is desirable to form a high tensile strength transmission wire. A method in the art achieves this by winding a transmission cable around a strength wire. However, such transmission cables are large in sectional area and low in flexibility. Therefore, any technique for providing for the extra length of transmission cable, especially those transmission cables having connectors, must accommodate for the extra space requirement of large cross section, low flexibility transmission cables.
During the installation of a transmission cable, it sometimes becomes necessary to draw out or draw in the transmission cable while the transmission cable is connected to a communications network; for instance, when moving the transmission cable transmission box or when constructing a building. This requirement occurs most frequently with a so-called "drop transmission cable" which is laid between a subscriber and a branching point on a communication pole. In order to meet this requirement, the extra length of transmission cable which can be wound or unwound should be at least 10 m. The transmission cable termination box for dealing with this extra length remains connected to the communication line. Therefore, in order to allow for wide use of a transmission cable termination box, it is essential that it be small in size and low in manufacturing cost.